Technical Field
The present invention relates to a display device and more particularly to a cover window with improved reliability and a foldable display device including the cover window.
Discussion of the Related Art
As information technology and mobile communication technology have been developed, a display device being capable of displaying a visual image has also been developed. Flat panel display devices, such as a liquid crystal display (LCD) device and an organic light emitting display (OLED) device, are developed and used.
In general, an LCD device includes a liquid crystal panel, which includes upper and lower substrates and a liquid crystal layer therebetween. The liquid crystal layer is driven by an electric field induced between a pixel electrode and a common electrode to display images.
An OLED device includes an organic emitting diode which includes an anode, a cathode and an organic emitting layer therebetween. In the organic emitting diode, holes and electrodes respectively from the anode and the cathode are combined such that light is emitted from the organic emitting layer to display images.
Recently, a foldable display device, which is fabricated by using a flexible substrate, is in demand. The foldable display device may be folded to be portable and may be unfolded to display images. Namely, with the foldable display device, a large-sized image display can be provided, and portability of the display device is improved.
FIG. 1 is a schematic cross-sectional view of a foldable display device according to the related art.
As shown in FIG. 1, the foldable display device 1 includes a display panel 10, a backplate 20 and a cover window 30.
When the display panel 10 is a light emitting diode panel, the display panel 10 may include a flexible substrate, a light emitting diode on the flexible substrate and a thin film transistor (TFT) for driving the light emitting diode.
For example, the organic emitting diode may include an anode, which is connected to the TFT, an organic emitting layer on the anode, and a cathode on the organic emitting layer. In addition, an encapsulation film for preventing moisture penetration may cover the light emitting diode.
On the other hand, when the display panel 10 is a liquid crystal panel, the display panel 10 may include a TFT on the flexible substrate, a pixel electrode, which is connected to the TFT, a counter substrate, which faces the flexible substrate, a common electrode, which is on the flexible substrate or the counter substrate, and a liquid crystal layer between the flexible substrate and the counter substrate. The display panel 10 may further include a backlight unit.
With a carrier substrate (not shown) attached to a lower surface of the flexible substrate, elements such as the TFT are formed on the flexible substrate, and the carrier substrate is released to obtain the flexible display panel 10.
In the flexible display panel 10, since the flexible substrate is thin, the backplate 20 for supporting the display panel 10 is disposed under the display panel 10.
The cover window 30 is attached to an upper side of the display panel 10. The damage on the display panel 10 from outer impacts is prevented by the cover window 30. Although not shown, the cover window 30 may be attached to the display panel 10 by an adhesive layer. For example, the cover window 30 may be formed of a tempered glass or high-hardness plastic.
In the related art foldable display device, when the folding and unfolding operation is repeated in the foldable display device 1, damages, e.g., cracks, may be generated in the cover window 30 such that the display quality and reliability (durability) of the cover window 30 and the foldable display device 1 are decreased.